This invention relates to an arrangement consisting of a photodiode and an optical fiber, to a circuit board on which a fiber with a photodiode is fastened and which contains a control circuit for the photodiode, and to a method of coupling an optical fiber to a photodiode.
In optical data communications, optical fibers are used as light guides. Receivers are photodiodes to which one end of the light-guiding fibers is coupled. The coupling between fiber and photodiode is of great importance. Conventionally, mechanical parts are used to hold the fiber and the photodiode in an optimum position relative to each other.
U.S. Pat. No. 6,017,681 discloses an arrangement in which the photodiode and the fiber are fixed to a substrate. A photosensitive material is then deposited between the fiber and the photodiode, and during the setting of the material, light is applied from the fiber to the material. This changes the optical properties of the photosensitive material in such a way that it forms a coupler between fiber and photodiode.
The mechanical parts that hold the photodiode and the fiber in position relative to each other must be formed with high precision because the permissible alignment tolerances are in the range of a few micrometers. This makes the mass production of the mechanical parts complex and expensive.
It is therefore an object of the present invention to provide an arrangement consisting of a photodiode and an optical fiber wherein good coupling is achieved in a simple manner. Another object of the invention is to provide a circuit board equipped with a photodiode and a control circuit for the photodiode on which an optical fiber is fastened which is coupled to the photodiode in a simpler manner. A further object of the invention is to provide a less complex method of coupling a fiber to a photodiode.
The object is attained by an arrangement of a photodiode and an optical fiber. The photodiode is mounted on a submount and contacted by at least one contact wire. The photosensitive surface of the photodiode is attached directly to one end of the optical fiber by an optically transparent adhesive.
In another aspect of the present invention, the object is attained by a circuit board having an optical fiber fastened thereon. The photosensitive surface of a photodiode is directly attached by an optically transparent adhesive to the end of the fiber. The photodiode is contacted by at least one contact wire which is connected to the circuit board. The circuit board is fitted with semiconductor components which form a control circuit for the photodiode. The adhesive joint between fiber and photodiode represents the only mechanical attachment of the photodiode. Preferably, a silicone pad is arranged between the submount and the circuit board.
According to the invention, the method of coupling an optical fiber to a photodiode comprises the steps of mounting the photodiode on a submount, contacting the photodiode by means of at least one contact wire, and attaching the photosensitive surface of the photodiode (PD) to one end of the optical fiber using an optically transparent adhesive.
Further developments of the invention are apparent from the dependent claims.
Particular advantages of the invention are that the dependence on temperature variations is reduced, that the arrangement is free of mechanical stress, that compared with conventional arrangements, photosensitivity is increased by about 10%, that very short leads can be used, which is important for applications at high bit rates (gigahertz range), and that the arrangement can be made very compact. The invention is also ideally suited for circuits with two or more photodiodes and fibers.